If in Christ the Kingdom of God "is near" and indeed present, definitively in the history of humanity and the world, at the same time its fulfilment continues to belong to the future. And so Jesus commands us to pray to the Father, "Thy Kingdom come" (Mt 6:10).
4. We must keep this question in mind as we deal with the Gospel of Christ as the "good news" of the Kingdom of God. This was the "guiding" theme of Jesus' proclamation, which speaks of the Kingdom of God above all in his numerous parables. Particularly significant is the parable that presents the Kingdom of God as a seed that a sower sows in the ground he has cultivated (cf. Mt 13:3-9). The seed is destined to "bear fruit" by its own virtue, without doubt, but the fruit also depends on the soil in which it falls (cf. Mt 13:19-23).
5. On another occasion, Jesus compared the Kingdom of God (the "Kingdom of Heaven" according to Matthew) to a mustard seed, which "is the smallest of all seeds," but once it has grown, it becomes a leafy tree, in whose branches the birds of the air find shelter (cf. Mt 13:31-32). He also compares the growth of the Kingdom of God to "yeast" that ferments flour so that it becomes bread to feed people (cf. Mt 13:33). However, Jesus also dedicates another parable to the problem of the growth of the Kingdom of God in the soil that is this world, that of the good wheat and the weeds sown by the "enemy" in the field sown with good wheat (cf. Mt 13: 24-30). Thus, in the field of the world, good and evil, symbolised by wheat and weeds, grow together "until the harvest", that is, until the day of divine judgement: another significant allusion to the eschatological perspective of human history. In any case, it tells us that the growth of the seed, which is the "word of God," is conditioned by how it is received in the field of human hearts: this determines whether it produces fruit and yields "a hundredfold, sixtyfold, or thirtyfold" (cf. Mt 13:23) according to the dispositions and responsiveness of those who receive it.
[Pope John Paul II, General Audience, 27 April 1988]